The role of an automatic fire extinguishing installation implementing sprinklers is to detect, as early as possible, the seat of a fire then to automatically trigger the extinction system, at least locally, this while emitting an alarm. The installation has for objective to contain the fire as much as possible, before the arrival of the fire brigade which then takes over the installation in order to extinguish the fire.
In the field of the invention, firefighting installations are classified into three categories, namely:                “wet-pipe” systems;        “dry-pipe” systems;        “vacuum” systems.        
In these three systems, the sprinklers are mounted in a network in such a way as to be distributed evenly over the site to be protected. Conventionally, the sprinklers comprise:                a fixing connector, that allows the sprinkler to be connected to pipework, with this fixing connector having a nozzle intended for the passage of water to be released in order to extinguish the fire;        a fusible member;        a shutoff member for shutting off the nozzle, held in the shutoff position by the fusible member.        
The fusible member is calibrated to blow when a certain temperature has been exceeded, as such releasing the nozzle from its shutoff member.
In “wet-pipe” systems, the entire piping of the installation is filled with water, and this up to the sprinklers. The water is therefore on standby behind the shutoff means and when the fusible member blows, the water flows through the nozzle of the connector of the sprinkler of which the fusible member has blown.
The release time for the water is therefore immediate, which is particularly advantageous. On the other hand, “wet-pipe” systems, are not adapted for sites that have risks of freezing. Indeed, in case of freezing, the water cannot flow. In addition, the freezing can cause deteriorations to the piping of the installation (deformation and even bursting of the pipes). In certain cases, the installation is emptied of water. In other cases, the site to be protected is heated in order to prevent any risk of freezing. For sites to be protected that have a relatively substantial surface area, the consumption of energy, and consequently the heating bill, can be substantial, and even prohibitive. Another way to fight freezing is to add an antifreeze agent to the water of the installation, such as glycol which is a toxic and carcinogenic product.
In the “dry-pipe” systems, the entire installation is emptied of water. The entire piping of the installation is kept under pressure. When the fusible members blow, the air pressure is released by the sprinkler or sprinklers in question and the water, also under pressure, tends to “push” the air outside of the installation until it arrives at the orifice or orifices released in such a way as to escape through the latter.
With such a system, the water can in certain cases take up to 60 seconds to reach the sprinkler of which the fusible member is blown, which is of course compliant with the current standard but which can be excessively long with regards to certain incipient fires.
In addition, “dry-pipe” systems do not entirely overcome the problems linked to freezing. Indeed, condensation can be created in the piping of a “dry-pipe” installation, which can damage certain components of the installation and cause the protection to fail.
Generally, “wet-pipe” and “dry-pipe” systems have the following disadvantages:                they are subject to forming slush and, consequently, to clogging;        they are subject to corrosion, which can obviously lead to an installation partially or entirely out of use and cause the protection to fail;        they can be the object of water leaks that cannot be seen;        they allow the development of microorganisms in the pipes of the installation.        
This results in that they require, among other things, antifreeze and anticorrosion treatments (involving recourse to harmful products).
Moreover, they require rinsing operations after use.
Furthermore, they imply putting into service times that are relatively long, according to the extent of the installation, which can range from one to four hours for “wet-pipe” systems and two hours and more for the “dry-pipe” systems.
In order to overcome all of these disadvantages, “vacuum” systems were designed. In “vacuum” systems, a vacuum is created in the pipes extending between a general valve and all of the sprinklers. In other terms, all of the pipes separating the valve from the sprinklers are in a vacuum.
In these systems, the vacuum constitutes an active energy which is used as a functional source in monitoring sprinklers. Indeed, if a fusible member of one of the sprinklers blows, the atmospheric pressure reaches the entire installation, which causes a change in the state of an actuator which, in turn, opens the general water inlet valve. Then the water quickly and without any obstacle invades the entire installation until the sprinklers, with the water flowing through the sprinkler or sprinklers of which the fusible member has blown. The vacuum which is still active in the networks quickly attracts the extinguishing water towards the sprinklers of which the fusible member has blown.
The triggering time of the actuator is very short, in that, when a fusible member blows, the “vacuum” installation immediately generates an aspiration phenomenon of the air outside of the installation. Note that this aspiration can be beneficial, as the aspiration effect on the seat of the fire tends to reduce the intensity of the latter.
The time for the water to arrive at the sprinkler of which the fusible member has blown is less than 60 seconds.
It is therefore understood that, due to the absence of water or of condensation in a “vacuum” system installation, the following results are obtained:                no corrosion, therefore no slush forming or clogging;        the guarantee of obtaining the density of extinguishing water required;        no development of microorganisms;        no water leaks possible (as the water is by default absent in the pipes of the installation that lead to the sprinklers);        no need for antifreeze agent or anticorrosion treatment;        no rinsing required before the installation is put into service.        
Furthermore, as shall be explained in more detail in what follows, the time for putting an installation with a “vacuum” system into service takes place extremely quickly, under about one minute.
Conventionally, a sprinkler comprises:                a fixing connector, that allows the sprinkler to be connected to pipework, having a nozzle through which the water is intended to flow in case of triggering of the sprinkler;        a fusible member;        a shutoff member for shutting off the nozzle, held in the shutoff position by the fusible member.        
The operation of these sprinklers is well known to those skilled in the art. The fusible member is constituted by an ampoule enclosing a liquid and an air bubble; when the fusible member is subjected to a predetermined temperature, the air bubble expands to the point of bursting the ampoule, which then releases the shutoff member from the retaining force exerted until then by the fusible member.
In “wet-pipe” systems, the water pushes the shutoff member and ejects the latter. In “dry-pipe” systems, it is the air which exerts a thrust in a first time on the shutoff member in order to eject the latter.
In “vacuum” systems, the means for ejecting are mounted on the sprinklers in such a way as to eject the shutoff member from its shutting-off position, in order to overcome the aspiration phenomenon which tends to keep the shutoff member in shutting-off position.
However, the flow of water by sprinklers necessarily implies that the shutoff member leaves its shutting-off position and that, consequently, the fusible member allows it to leave this position, and this by blowing.
However, in certain cases, it is desired to be able to trigger the flow of water through sprinklers, even when the temperature in the vicinity of the sprinklers has not reached the threshold at which the fusible member blows. In other terms, it is sought to protect in certain cases, by anticipation, a zone of the site to be protected although the fire is still distant from the zone in question. This can be the case for example for:                protecting shelving, by creating a protection perimeter around the shelving;        open passages, in order to create a curtain of water;        specific reservoirs to be maintained at temperatures below a predetermined threshold.        